1. Field of the Invention
The present invention relates to an electronic apparatus controllable with a microcontroller.
2. Description of the Prior Art
In various electronic apparatus such as copier, the use of microcomputer for sequence timing control has become quite common because of excellent performance and flexibility in circuit control. However the microcomputer is principally employed for timing control so that, in the control of a copier, there are employed at least two microcomputers for the general sequence control and for the motor control.
FIG. 1 shows a copier as an example of the electronic apparatus in which the present invention is applicable. Said copier is provided with two motors respectively for main drive (photosensitive drum, sheet feeding, sheet transportation etc.) and for driving the optical system. The principal function of the copier is governed by said two DC motors, though the copier naturally contains other motors such as a cooling fan motor, a sheet transporting motor, and a fixing roller motor.
In the following there will be given an explanation on the structure of said copier, while making reference to FIG. 1. On a lateral end of the main body 21 of the copier there are provided two sheet cassettes 22, 23, and a sheet discharge tray 24 is provided on the other lateral end. Around a photosensitive drum 25 there are provided, as illustrated, a corona charger 46, an erasing lamp 47, an optical system 48, a developing roller 9, a transfer charger 10, a cleaning device 11 and a pre-exposure lamp 12. On the upper face of the main body 21 there is provided a glass plate 13, and an original document placed thereon is illuminated by an exposure lamp 14. The reflected light passes a lens system 15 and is guided to the aforementioned optical system 48, The sheets in the sheet cassettes 22, 23 are guided by feed rollers 16, 17 to registration rollers 18, and, after the transfer of a toner image from said photosensitive drum 25 by means of the aforementioned transfer charger 10; the sheet is transported by a conveyor belt 19 to fixing rollers 20 and is finally discharged to the tray 24.
A main motor 1 for driving the drum, transporting system, fixing system and other mechanical parts other than the optical system is composed of a DC servo motor for obtaining a constant speed. An optical system driving motor 2 is composed of a DC servo motor. A suction motor 3, composed similarly of a DC motor, is used for adhering the sheet onto the conveyor belt 19 to carry the sheet to a fixing station. In the present apparatus all the driving motors are composed of DC motors for avoiding the trouble of change in the gear ratio change associated with the change in the power supply frequency 50 Hz or 60 Hz. The use of DC motors, which are smaller in size and higher in the output torque than AC motors, has become quite common in motor-controlled electronic apparatus.
Now there will be explained the function of the above-described apparatus. When the power supply is turned on, there is conducted initialization of the photosensitive drum by cleaning thereof and by removal of the surface potential by the preexposure lamp, thus obtaining a uniform surface potential. When a heater in the fixing station 20 reaches a predetermined temperature, a display indicating the operable state is given in an unrepresented operation unit. In this state the operator selects the sheet size and the copy number, and depresses a copy start button. Upon depression of said copy start button, a sheet of the selected size is supplied from the cassette 22 or 23 and reaches the registration rollers 18 to align the front end. In the meantime the sheet size is detected by counting the sheet running time, for example, with reflective photosensors arranged according to the sheet sizes, in order to effect the blank exposures on the leading, trailing and lateral ends of the photosensitive member according to thus obtained sheet size thereby avoiding deposition of toner outside the image area. Also in the course of the scanning motion of the optical system, the density and the size of the original are read by unrepresented photodiodes and are fed back on real time basis for illumination and bias control to automatically control the copy density. Said feed back is made to an unrepresented developing bias control circuit to regulate the developing bias, thus automatically optimizing the image density.
On the other hand the original scanning optical system is controlled by a servo motor and scans the original with a doubled speed for a full length or a half length according to the data of sheet size detection.
Subsequently to the image formation explained above, the sheet which have received the transferred image is subjected to image fixation in the fixing station 20 and is discharged to the tray 24.
In the following there will be explained an example of the control of speed and position of the motors employed in the copier. FIG. 2 shows the principle of the phase locked loop (PLL) system employed in the servo control. A signal f.sub.L0 from a reference oscillator V.sub.CO and a reference frequency signal f.sub.R are supplied to a phase comparator, and an error voltage V.sub.E is supplied back to the oscillator V.sub.CO through a low-pass filter LPF for eliminating the high frequency components. The error voltage V.sub.E is not generated when the phases of f.sub.V and f.sub.R are mutually equal. If f.sub.V and f.sub.R are different, an error voltage V.sub.E is generated to vary the oscillation frequency f.sub.V0 of the oscillator V.sub.C0. Said variation continues until the error voltage becomes zero, namely until the phases of f.sub.V and f.sub.R become mutually equal.
FIG. 3 shows an example of motor servo control utilizing the above-described principle. The control system is composed, as shown in FIG. 3, of a phase comparator, a low-pass filter LPF, an amplifier AMP, a motor M and an encoder ENC. The phase comparator compares a command signal S.sub.1 with a feedback signal S.sub.2 to generate an error signal. In case the command signal S.sub.1 and the feedback signal S.sub.2 are composed of continuous AC signals, the output of the phase comparator is given by: EQU V.sub.c =K.sub.m S.sub.1 S.sub.2 ( 1)
The AC command signal S.sub.1 can be represented by: EQU S.sub.1 =-V.sub.s cos.theta..sub.i.
The angle .theta..sub.m of the motor shaft is related to the electric angle .theta..sub.o of the encoder ENC by .theta..sub.o =n.theta..sub.m, wherein n represents the number of pulses generated by the rotation of the encoder. On the other hand, the feedback signal S.sub.2 is represented by: EQU S.sub.2 =V.sub.0 sin.theta..sub.o
so that the output of the phase comparator in (1)
can be rewritten as: EQU V.sub.c =-K.sub.m V.sub.s V.sub.o cos.theta..sub.i sin.theta..sub.o (2)
which is further modified as: EQU V.sub.c =K.sub.m V.sub.s V.sub.o /2 [sin(.theta..sub.i -.theta..sub.o)-sin(.theta..sub.i +.theta..sub.o) ] (3) Since sin(.theta..sub.i +.theta..sub.o) is a high-frequency component and is cut off by the low-pass filter LPF, the equation (3) becomes V.sub.c =K.sub.p sin(.theta..sub.i +.theta..sub.o) wherein K.sub.p =K.sub.m V.sub.s V.sub.o /2. Also the phase difference .theta..sub.e is given by:
.theta..sub.e =.theta..sub.i -.theta..sub.o
so that the equation (3) can be approximated as:
V.sub.c =K.sub.p (.theta..sub.i -.theta..sub.o)=K.sub.p .theta..sub.e
thus giving rise to a simplified model as shown in FIG. 3. The output of the phase comparator can therefore be approximated as the sum of two components.
Now reference is made to FIG. 4 showing an example of circuit utilizing the above-explained principle The microcomputer employed is a multiprocessor system involving two microprocessors MPU1, MPU2 composed of Intel 8051's, of which MPU2 for motor control alone is illustrated. For speed and position control, the servo motor generally requires constant counting of pulses from the encoder. Consequently, the use for this purpose of a common microprocessor which is also used for sequence control is inadequate for real-time control and may give rise to an erroneous operation. Consequently there are employed two microcomputers, of which unrepresented one MPU1 is used for sequence control while the other one MPU2 controls the main motor DCM1 and the optical scanning motor DCM2 through optical encoders OPE1, OPE2. The MPU1 and MPU2 are mutually synchronized through a serial communication interface and achieve mutual interfacing through bit-pattern protocol. The MPU1 will be further explained later.
In FIG. 4, timing pulses are generated by a rotating disk fixed on the shaft of the main motor DCM1 and are supplied to an event counter. Said pulses have a determined ratio, for example 1/10, to pulses generated by a frequency generator FG for servo control fixed on the shaft end of the main motor and generating for example ca. 200 pulse per turn of the motor.
As explained in the foregoing, a multi-chip structure has been indispensable for real-time control of a copier, and such multi-chip structure has been inevitably complex because of the required interfacing between the MPU's.
In addition, such structure inevitably require LSI's for servo control, and analog IC's such as D/A converter, F/V converter, comparator etc., which raise the cost of the entire system. Also the complicated control circuit requires a prolonged time in designing and debugging, reduces the reliability of the system and requires an increased space.